1. Field of the Invention
The present invention relates to a medical implantable lead having a header arranged at a distal end thereof and a radiopaque ring arranged at the header.
2. Description of the Prior Art
A lead of the type mentioned above typically has a lumen extending between its ends and an electrode extending through the lumen. In order to be able to securely connect the electrode to body tissue a helical fixation element, also called helix, is arranged at the distal end of the electrode. The helix is extendable and retractable within the lumen by means of rotating the helix. The tip of the helix is sharp in order to easily penetrate body tissue. In order to be able to provide good guidance to a user who is going to fasten the helix in the body tissue, a radiopaque ring is applied as close to the distal end of the header as possible. The ring is used as a marker, or position reference, for the position of the helix.
One example of such a lead is disclosed in U.S. Pat. No. 7,092,766, Salys et al. The lead is provided with a collar, which is a radiopaque ring, at the very distal end of the lead. The collar is welded to the header, which extends proximally of the collar. It is a desire, for many reasons including avoiding shatter-noise due to electrical contact between the helix and the metal header, increasing electrode impedance, and providing good properties of interaction with the body tissue, to form the header from a polymer and having such a polymer header define the very distal end portion of the lead. Then it will not be possible to weld the header with the radiopaque ring, but it will be necessary to use an adhesive. Then a question arises regarding how to arrange the radiopaque ring to minimize potential new problems of the adhesive fastening of the ring to the header. Also there is a general question about how to arrange the radiopaque ring at the header close enough to the distal end to maintain a good guide function.